1. Field of the Invention
A durable, heat-resistant functional hydrophobic, hydrophilic, or reactive coating deposited using vapor deposition techniques on a variety of substrate materials.
2. Description of the Related Art
This section describes background subject matter related to the invention, with the purpose of aiding one skilled in the art to better understand the disclosure of the invention. There is no intention, either express or implied, that the background art discussed in this section legally constitutes prior art.
Substrate materials, micro structures, and components coated with hydrophobic and hydrophilic films have, in recent years, found many applications in a variety of industries including automotive, semiconductors (SEMI), micro-electro-mechanical systems (MEMS), bio- and micro-fluidics, nano-imprint lithography (NIL), and others. The main motivation and purpose of such coatings is the desire to obtain a specific surface property and/or protection of the material surface without changing the base substrate material itself. For example, self-assembled monolayers (SAM) formed from hydrocarbon and fluorocarbon coatings provide hydrophobic surfaces characterized by a very low surface energy and low reactivity. Such films prevent wetting, improve de-wetting, and facilitate cleaning in the case of e.g. glass and automotive industry parts. SAM coatings are also used to prevent stiction in MEMS and NIL applications, and can enhance protection from moisture and environmental contamination in packaging of semiconductors and display devices. Conversely, hydrophilic films are used in applications where an improvement in surface wetting is desired, such as in the case of microfluidic devices, bio-chips, anti-fog and other related applications.
The liquid and vapor phase coating techniques known to provide such functional surfaces frequently include substrate surface silanization using silane based precursors. The most commonly used substrate surface reaction mechanisms for silane precursor attachment are hydrolysis of a chlorosilane and its reaction with hydroxyl groups present on the substrate surface. Another possibility is the attachment of an amine terminated alkylsilane to the substrate surface. Particularly, covalent reaction with the substrate surface, whether with hydroxyl groups or other groups which are strongly attached to the substrate surface, provides a strong bonding of the silane to the substrate surface. Covalent bonding provides a relatively high mechanical and chemical stability of the films. With respect to reaction with hydroxyl groups, this reaction requires a high concentration of the hydroxyl groups on the substrate surface, and is therefore limited to substrates exhibiting such groups, e.g. silicon, quartz, and various oxides.
Deposition of SAM functional coatings on substrate materials other than those exhibiting a high concentration of hydroxyl groups may be achieved using an adhesion layer-forming precursor. Many of these precursors form non-covalent bonds with the substrate material surface, and typically the overall coating structure including the adhesion layer with SAM attached exhibits a relatively inferior durability. This is particularly true when there is mechanical abrasion of the exterior, SAM-coated surface.
The use of specialized adhesion promoting layers, which adhere well to particular substrate materials and provide a high concentration of hydroxyl groups for subsequent reaction with a silane-based hydrophilic or hydrophobic coating precursor which is in vapor form (by way of example and not by way of limitation), has been proposed. Adhesion layers of silicon oxide or various metal oxides have been used because these exhibit a high density of surface hydroxyl states. Adhesion of a silicon oxide or metal oxide layer to the substrate material, as well as quality and durability of the top functional layer applied over the adhesion layer determine the ability of a SAM-coated surface to meet the demanding requirements in commercial applications. In commercial applications, the SAM-coated surface undergoes prolonged exposure to manufacturing and environmental factors such as: radiation, liquid immersion, mechanical friction, or high temperature.
In U.S. Pat. No. 7,638,167, issued Dec. 29, 2009 titled “Controlled Deposition of Silicon-Containing Coatings Adhered by an Oxide Layer”, and in Application Ser. No. 11/978,123 filed Oct. 26, 2007 (Pub. No. 2008-0081151A1) (now abandoned), titled “Vapor Deposited Nanometer Functional Coating Adhered By An Oxide Layer”, Kobrin et al. described methods of depositing functional SAM coatings using oxide films as adhesion layers on various substrates. The minimum thickness of the silicon dioxide adhesion layers grown by molecular vapor deposition (MVD) was said to be dependent on the substrate material used. Films as thick as 200 Å were required in the case of some substrate materials to assure relative stability of the adhesion layer—upon water immersion. Metal oxides and in particular aluminum oxide and titanium oxide coatings were proposed as adhesion layers.
With regard to the use of metal oxide films in electronic device packaging, Featherby et al., in U.S. Pat. No. 6,963,125 issued Nov. 8, 2005, and entitled “Electronic Device Packaging” described an encapsulation method consisting of two layers: 1) an inorganic layer which prevents moisture intake and 2) an outside organic layer protecting the inorganic layer, in which both layers are said to be integrated with an electronic device plastic package. The organic layer which is applied directly over the inorganic layer is said to be preferably Parylene C (Col. 10), which is a relatively thick material, expensive, and is said to serve the function of protecting the brittle inorganic coating during manufacturing steps such as injection molding.
The use of dual layer films containing ALD alumina and a thin alkylaminosilane functional SAM coating attached to alumina was proposed for wear and stiction protection in MEMS by George et al. in U.S. Pat. No. 7,553,686, entitled “Al2O3 Atomic Layer Deposition to Enhance the Deposition of Hydrophobic or Hydrophilic Coatings on Micro-electromechanical Devices”. In addition, George et al., in U.S. application Ser. No. 10/482,627 filed on Jul. 16, 2002 (Pub. No. US 2004/0194691), and entitled “Method of Depositing an Inorganic Film on an Organic Polymer”, described the use of an ALD metal oxide films as moisture and gas barriers on polymeric substrates.
With the development of electroluminescent devices, flat panel displays, organic light emitting diodes (OLEDs), and flexible electronics there is even a stronger need to protect such devices from performance degradation due to oxygen and moisture. PVD and ALD alumina films have been tried extensively for such applications, however, the single or dual layer protective coatings of the kind described above have been found to be inadequate.
Various multilayer film laminates have been explored as a hermetic glass package replacement for use in OLEDs. For example, Haskal et al. in U.S. Pat. No. 5,952,778, issued Sep. 14, 1999, entitled “Encapsulated Organic Light Emitting Device” proposed an encapsulation scheme to prevent the OLED device from oxidation and degradation due to ambient oxygen and water. The protective encapsulation comprises three contiguous layers: a first layer of passivation metal such as gold, silver, indium, aluminum or transition metal; a second layer of thin film deposited dielectric material such as silicon dioxide or silicon nitride; and, a third layer of a hydrophobic polymer. Park et al., in U.S. Pat. No. 6,926,572, issued Aug. 9, 2005, entitled “Flat Panel Display Device and Method of Forming Passivation Film in the Flat Panel Display Device” proposed the use of an organic insulating film and/or a metal film in combination with an inorganic insulating film to provide a two layer or three layer passivating film (claim 14, for example). In particular, the reference teaches that it is possible to additionally form an organic insulating film before and/or after the inorganic insulating film is formed (Col. 3, lines 47-50). Typically, the organic insulating film is said to be deposited by TCVDPF (thermal chemical vapor deposition polymer formation). When a metal film is part of the passivating film, it is proposed that the metal film is the first layer of a two or three layer passivation film, deposited over a cathode electrode which makes up part of the organic light emitting device (Col. 4, lines 48-57).
Despite efforts like those described above, the functionality of the passivating coatings developed has been lacking, and the cost of the thick multilayer films proposed is high. The search for a better-performing and thinner protective films which meet cost and performance requirements continues, in an effort to commercialize a multitude of prototype devices in volume production.